How to Measure a Window Size in 4 Simple Steps

September 20, 2024

Is it time to replace your windows?

Do you want to improve energy efficiency?

Maybe you just want to spruce up your space with new blinds or window screens. Whether you’re planning a full set of replacement windows or just looking to add a little something new, knowing how to measure a window size can make all the difference, saving you time, effort, and money.

Before You Start

Before you begin measuring your windows, make sure you have the right tools on hand. Here’s what you’ll need:

Tape measure: A steel measuring tape that locks in place works best for accuracy.
Pencil and notepad: To avoid errors, jot down all measurements as you go.
Level: A small level will help you check for squareness and alignment.
Ladder: For taller or hard-to-reach windows, a sturdy ladder is a must.
Measuring assistant: It’s useful to have someone hold the other end of the tape measure for larger windows, if you can.

You’ll also want to familiarize yourself with these window terms before you start measuring:

Frame: The rigid structure that holds the window in place, including the top, bottom, and sides.
Sill: The horizontal bottom part of the window frame where the window sits.
Jamb: The vertical sides of the window frame that run up and down the sides.
Depth: The thickness of the window frame from front to back.

1. Measure Window Width

Width is one of the easiest measurements, so it’s a good place to start when you’re measuring a window size. You’ll want to take three width measurements:

Measure the top: Place your tape measure across the window from jamb to jamb at the very top. Make sure you measure the inside of the frame, not the trim or outside.
Measure the middle: Measure across the middle of the window, where bowing or slight shifts in the frame could occur.
Measure the bottom: Take a final measurement across the bottom, just above the windowsill.

Windows are often slightly irregular, so record the smallest of the three measurements as your width to be sure the window will fit. Avoid measuring over any old caulking, seals, or decorative trims, and double-check all measurements to avoid mistakes.

2. Measure Window Height

Getting the correct height is just as important as width. A window that’s too short or tall will either not fit or leave gaps that compromise insulation or privacy. Here’s how to measure:

Measure the left side: Place your tape measure vertically from the inside top of the frame to the bottom of the sill.
Measure the center: Measure again down the middle of the window. Sometimes, windows can sag or warp slightly in the middle, so this measurement is important.
Measure the right side: Finally, measure the window height along the right side.

Just like with width, always use the smallest height measurement to ensure the best fit. Measure from the inside of the frame, not the trim or wall. And if the window has a sloped sill or trim, make sure you measure to the exact point where the window meets the sill.

3. Measure Window Depth

Depth measures how thick your window frame is from front to back. It’s easy to overlook when you’re thinking about how to measure a window size, but it’s especially important for window replacement and energy-efficient windows. The steps for measuring window depth are:

Open your window to measure inside the frame: Place your tape measure between the interior edge of the window frame and the exterior edge, making sure to measure inside the jamb.
Take measurements at different points: Window frames can sometimes be uneven in depth, so measure at the top, middle, and bottom.

Again, you’ll use the smallest depth measurement to ensure the window fits properly. Don’t include any existing window treatments or external coverings in your depth measurement.

4. Check for Square Alignment

Square alignment in a window means that all corners form perfect 90-degree angles. Windows that aren’t perfectly square can have issues with leaks, gaps, or energy efficiency. While measuring your window’s size, check for squareness using these steps:

Measure diagonally: Measure from the top left corner of the window to the bottom right corner. Then, measure from the top right corner to the bottom left.
Compare the measurements: If both diagonal measurements are the same, your window is square. If not, your window may be slightly skewed, and you’ll need to factor this in when ordering new windows or treatments.

A small difference (around 1/8 inch) is usually acceptable and can be compensated for during installation. Larger discrepancies might need a professional touch to make sure everything fits properly.

How to Measure a Window Screen Size

The steps for how to measure a window screen size are similar, but where you’ll measure is different: The size of a window screen is measured based on the interior dimensions of the screen frame, which fits into the window opening, rather than the full window frame. Screens also allow for a small gap around the edges so you can easily remove them. Here’s what to do:

Measure width: Place your tape measure across the inside of the screen frame to get the width.
Measure height: Measure from the top to the bottom of the screen frame.
Check frame thickness: Measure the thickness of the screen frame to ensure a snug fit in your window frame.

Always measure the existing screen or the inside of the window frame where the screen will sit. Getting the measurements wrong can lead to ill-fitting screens that won’t keep out bugs and dirt.

Considerations for Specialty Windows

Specialty windows like bay windows or arched windows add character and natural light to your home. Because of their unique shapes, they can be tricky to measure accurately. Follow these tips for better results:

Bay windows: When measuring bay windows, treat each section as a separate unit. Measure the width, height, and depth of each individual window and the angle at which the windows connect.
Arched windows: First, measure the width at the base of the arch, then measure the height from the bottom of the frame to the top of the arch’s peak. Make sure to also measure the arch’s curve using flexible measuring tape to account for the specific shape.
Skylights: You’ll need to measure both the interior opening and the exterior frame to ensure a watertight fit. Skylight depth is especially important because it needs to accommodate roof insulation and flashing.

For any non-standard window shapes, consulting with a professional can save you time and costly mistakes from measurement mishaps.

The Importance of Accurate Measurements for Windows

Precision is key to measuring a window size and avoiding gaps, drafts, and poor fits. An improperly measured window can result in blinds that don’t fully cover the opening or new windows that require costly adjustments. On the other hand, precisely measuring your windows can:

Save money: Precise measurements reduce the chance of ordering the wrong size windows or treatments and prevent costly returns or modifications.
Save time: Correct measurements mean you can avoid delays caused by needing to reorder products or make last-minute adjustments.
Improve energy efficiency: Well-fitted windows prevent air leaks, saving you money on heating and cooling bills.
Make installation easier: You won’t need to fill in any gaps or deal with windows that don’t fit into the existing opening.

Get Professional Window Measurements

While you can learn how to measure a window size yourself, hiring a professional is often the best option. West Shore Home can help you with your entire window replacement project, from measuring and ordering to installation and cleanup.

We offer free design consultations and no-obligation estimates for your project, plus one-day installation and excellent financing options. Contact us today to schedule a consultation for your window replacement and get professional service you can trust.

How to Measure a Window FAQs

Can I use the same measurements for different types of windows?

No, each type of window may have different frame styles, depths, and installation requirements. Casement, double-hung, and bay windows, for example, often require specific measurements for proper fitting. Always measure each window individually to ensure accuracy and avoid issues with installation or functionality.

How does measuring a window size help with choosing replacement windows?

Accurate window measurements ensure you choose replacement windows that fit properly in your existing frame. Correct sizing prevents gaps, drafts, and installation issues, improving energy efficiency and appearance. Precise measurements also help in selecting custom window styles, materials, or treatments that perfectly match your home’s specifications.